1. Field of the Invention
The present invention relates generally to implantable medical devices, and more particularly relates to implantable medical devices for the treatment of obstructive sleep apnea.
2. Description of the Prior Art
The medical characteristics of sleep apnea have been known for some time. There are two generally recognized forms of the disease. The first is central sleep apnea which is associated with the failure of the body to automatically generated the neuro-muscular stimulation necessary to initiate and control a respiratory cycle at the proper time. Work associated with employing electrical stimulation to treat this condition is discussed in "Diaphragm Pacing: Present Status", by William W. L. Glenn, in Pace, Volume I, at pages 357-370 (July-September 1978).
The second condition is known as obstructive sleep apnea. It is discussed at some length in "Obstructive Sleep Apnea: Diagnosis and Treatment", by Drs. Cook and Osguthorpe in Journal of South Carolina Medical Association, 81 (12): 647-651 (December 1985).
At present, a tracheostomy may be the treatment of choice for a number of patients when obstructive sleep apnea is severe, although systems employing continuous positive air pressure (CPAP) are now available. However, some interest has been displayed in electrical stimulation of the muscle tissue along the upper airway during respiration. U.S. Pat. No. 4,830,008 issued to Meer discusses a technique for electrical stimulation of the muscles of the upper airway in synchrony with the respiratory cycle. U.S. Pat. No. 4,506,666 issued to Durkan discusses such stimulation in conjunction with pressurized airflow supplied by a respirator.
A key problem associated with electrical stimulation of the upper airway is detection of an apnea event. Some of the prior art systems apparently rely upon screening for employment of therapy. In these systems, the treatment is consistently applied without regard to a medical condition which might be intermittent. Yet other systems attempt to detect the onset of an apnea event using measurement of a parameter associated with apnea. The concern with such systems is in the accuracy of detection.